Merging [2+2] Cycloaddition with 1,6‐/1,4‐Aza‐Binucleophilic Additions toward Unprecedented Indazole‐Containing Polycycles

The first metal‐free [2+2] cycloaddition and 1,6‐/1,4‐aza‐binucleophilic addition cascade of yne‐allenone esters and cyclic aza‐binucleophiles was reported, leading to the atom‐economic protocol toward hitherto unreported indazole‐containing polycycles with one quaternary carbon‐amino functionality and good to excellent yields. The reaction pathway involves [2+2] cycloaddition, ring‐opening of fused cyclobutenes and 1,6‐/1,4‐aza‐binucleophilic addition sequence, resulting in continuous multiple bond‐forming events including C−C and C−N bonds to build up molecular complexity